1. Field of the Invention
The present invention relates to shape memory polymers and waterborne coating materials and, more particularly, to waterborne shape memory polymer coatings.
2. Description of the Related Art
Polymeric coating materials are extraordinarily important and used in a wide range of application fields such as building materials, vehicles, household products, beauty products, medical devices, etc., for the purpose of preventing rusting, adding colors, providing additional properties, etc.
Waterborne coating materials, especially waterborne polyurethane (WB-PU)-based coatings are becoming more and more important as a substitution of volatile organic solvent-borne coatings to reduce the volatile organic compounds (VOC) emission to the environment, and are increasingly being used for wood and automobiles as well as softer and/or more flexible materials such as textiles, leather, paper, and rubber.
Waterborne coating materials comprising polymer dispersions are used for various fields like building materials and household products to avoid air pollution and health hazards due to the volatile organic solvents that are also still commonly used for coating materials (as described above). For the dispersibility in water, charging groups are incorporated into the polymer chains. A couple of methods to prepare the aqueous polymer dispersion are known.
Shape memory polymers (“shape memory polymers” or “SMP's”) are a class of smart materials that offer mechanical action triggered by an external stimulus. More specifically, SMP's feature large-strain elastic response and extensibility, but temporary shapes can be “stored” through network chain immobilization by vitrification, crystallization or some other means. As a simple example, a complex three dimensional SMP shape can be compacted into a slender form by a cycle of heating to a rubbery state, elastically deforming this rubbery state, cooling to immobilize the network chains, and unloading. Later, application of heat, light, or solvent exposure can “trigger” a return to the equilibrium, complex shape through network chain mobilization.
In terms of macromolecular architecture, SMP's are responsive polymers comprising cross-linked network polymer backbones where the polymer backbones between cross-linking junctions are crystallizable or glassy and can behave as “switching segment.” SMP's can be fixed into a deformed temporary shape and later recover to a permanent shape memorized by the cross-linked network structure upon a stimulus, most commonly heat (as discussed above). Generally, SMP's are stiff materials at the shape-fixed state due to the primary mechanism of shape fixing, i.e., crystallization or vitrification of network polymer backbones, and a large force can be generated during the shape recovery.
Paper products are known, particularly absorbent fibrous structure products such as absorbent sanitary tissue paper, including tissue paper provided in roll form such as paper towels or toilet paper, and tissue provided in flat or folded from, such as for facial wipes. Sanitary tissue paper generally comprises absorbent cellulosic fibers, and is generally made in a wet-laid process in which the fibers are provided in an aqueous slurry onto a forming screen or belt, and subsequently dried. Fibrous structures can also be in the form of nonwoven materials comprising polymeric fibers. Nonwoven fibrous structures can be formed by fiber extrusion, or in wet- or dry-laid processes, as is known in the art.
Smart textiles with shape memory effect have attracted much attention in recent decades. It is believed that such smart textiles, including those comprising cellulosic fibers, can memorize their original shape because the cellulose chains are cross-linked and thus the wrinkles on the textiles formed during use can be easily removed after washing without pressing. A variety of cross-linking reactions in the cellulosic fibers have been invented, and most of them utilize volatile and irritant cross-linkers like formaldehyde or ammonium. A great deal of effort and care is required to remove the residues of unreacted cross-linking agents to avoid health hazard.
There is a continuing unmet need for methods providing textile materials with shape memory effect that is relatively long-lasting, reversible, harmless, and which effect can be rendered widely applicable for various substrates.
Further, there is a continuing unmet need for fibrous structures that can retain their shape after use, or beneficially change their shape during use, including after being wetted.
Additionally, there is a continuing unmet need for sanitary tissue products that have built-in shape memory, such that upon wetting, a tissue product can recover a certain amount of shape associated with the built-in shape memory.
Description of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section or elsewhere in this Application, these discussions should not be taken as an admission that the discussed publications are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section (as well as throughout the application), they are all hereby incorporated by reference into this document in their respective entirety(ies).